Piston Swap w/o splitting block???

[JWScarab]

Hi, I bought a project boat and the old owner had installed a rebuilt engine on it before I bought it. It wouldnt run right so after troubleshooting, I found it has 1 port and 1 starboard pistons swapped. The engine is rebuilt w/zero hours. Can I remove the connecting rod bolts thru the slots in the lower block and swap piston/rod/cap without splitting block? It looks "possible". Its a Mercury 1995 200EFI. Thanks so much!!!!

 

[j_martin]

Re: Piston Swap w/o splitting block???

It's possible, but very tricky. If the ace (spelled with a double $$) that rebuilt that engine couldn't keep port and starboard straight, I'd put her on the bench, tear it down, and check everything. No sense in breaking new parts and ventilating a perfectly good block. With any luck, you'll have assembled a real nice motor for the cost of a gasket set. If you're reel cheep, you might even be able to reuse the gaskets.

The most likely other mistake is mis-matching rods, getting the caps on wrong, or rod bolt torque. Any one of these will grenade the engine.

hope it helps.
John

 

[JWScarab]

Re: Piston Swap w/o splitting block???

Thanks John, yes it helps a lot! I am not sure what you mean by mismatched rods tho. I understand the caps and torque but how do I tell if a rod is properlt placed?

I have to think long and hard about this "gamble", as the powerhead comes off and the job got a lot bigger to do it right - which I agree would be the best. And I didn't mention it is a twin - the other motor runs great but the same guy did it, so my work is double with the do-it-right logic vs the piston swap and fingers crossed........

Any more input is welcomed please as I am new to Merc Outboards.....

Thanks all !!! Joe

 

[j_martin]

Re: Piston Swap w/o splitting block???

Might have depended on which beer he was on.

Rods are machined, then broken into rod and cap. The fracture has to be perfectly aligned when reassembled, or there is a step in the bore. The test is that you should not be able to feel the gap with a pencil tip. The motor will run till the bearing spalls, and then grenade or lock up, destroying rods, crank, and often the block.

hope it helps
John

 

[jimmbo]

Re: Piston Swap w/o splitting block???

Do not reuse the connecting rod bolts. They are one time only. Get new ones.

 

[JWScarab]

Re: Piston Swap w/o splitting block???

I pulled all 6 pistons out!! I've decided to tear it down due to my findings. One head bolt is from a bolt bin, with 4 washers to shorten it up. One piston has needle bearings that are 1/8-1/4" too short - they slop back and forth. The other 5 are full length. So I need to tear it down and do it right!!

I did the pencil test on the rods/caps. I cant feel them if I allign them perfectly, but I dont see how they will be alligned perfectly during assembly since you cant put your finger in there to help allign. Maybe the bearings will center the rod/cap?

I think this guy used 3.0L rods on the engine. The piston tops come exactly to the top of the block cylinder hole. Also 2 of the pistons are different - no markings on top - different p/n. And I think these were carb engines converted to EFI.

Wish me luck......lol.

 

[j_martin]

Re: Piston Swap w/o splitting block???

Now, ain't you glad you looked?

 

[JWScarab]

Re: Piston Swap w/o splitting block???

Yes, definitly! And thanks all for the advice to do it right. I am now on my way to tearing it down completly. I hope to use the same rods/caps/pistons but use new gaskets/head bolts/rod bolts - if I am lucky.

Not sure if rods were changed. The motors ran fine before (except 2 holes not firing). Most holes are clean and smooth. There are two cylinders that have slight axial scores. Hopefully hone them out and run with it.

I am not looking to biuld a perfect engine, but rather an engine that is done pretty much right, and that wont come apart, and will last.

Any thoughts - just yell!! I am learning - never done this before!